Power Management GuideDennis NienhüserChris WhiteJoshua Saddler
Power Management is the key to extend battery run time on mobile systems like
laptops. This guide assists you setting it up on your laptop.
1.442009-08-11Introduction

Capacity and lifetime of laptop batteries have improved much in the last years.
Nevertheless modern processors consume much more energy than older ones and
each laptop generation introduces more devices hungry for energy. That's why
Power Management is more important than ever. Increasing battery run time
doesn't necessarily mean buying another battery. Much can be achieved applying
intelligent Power Management policies.

A Quick Overview

Please notice that this guide describes Power Management for laptops.
While some sections might also suite for servers, others do not and may
even cause harm. Please do not apply anything from this guide to a server
unless you really know what you are doing.

As this guide has become rather long, here's a short overview helping you to
find your way through it.

The Prerequisites chapter talks about some
requirements that should be met before any of the following device individual
sections will work. This includes BIOS settings, kernel configuration and some
simplifications in user land. The following three chapters focus on devices
that typically consume most energy - processor, display and hard drive. Each
can be configured seperately. CPU Power Management
shows how to adjust the processor's frequency to save a maximum of energy
without losing too much performance. A few different tricks prevent your hard
drive from working unnecessarily often in Disk Power
Management (decreasing noise level as a nice side effect). Some notes on
graphics cards, Wireless LAN and USB finish the device section in Power Management For Other Devices while another
chapter is dedicated to the (rather experimental) sleep
states. Last not least Troubleshooting lists
common pitfalls.

Power Budget For Each Component

Nearly every component can operate in different states - off, sleep, idle,
active to name a few - consuming a different amount of energy. Major parts are
consumed by the LCD display, CPU, chipset and hard drives. Often one is able to
activate OS-independent Power Management in the BIOS, but an intelligent setup
in the operating system adapting to different situations can achieve much more.

Prerequisites

Before discussing the details of making individual devices Power Management
aware, make sure certain requirements are met. After controlling BIOS settings,
some kernel options want to be enabled - these are in short ACPI, sleep states
and CPU frequency scaling. As power saving most of the time comes along with
performance loss or increased latency, it should only be enabled when running
on batteries. That's where a new runlevel battery comes in handy.

The BIOS Part

First have a look into your BIOS Power Management settings. The best way is to
combine BIOS and operating system policies, but for the moment it's better to
disable most of the BIOS part. This makes sure it doesn't interfere with your
policies. Don't forget to re-check BIOS settings after you configured
everything else.

Setting USE Flags

Please check that the acpi USE flag is set in
/etc/make.conf. Other USE flags that might be interesting for your
system are apm, lm_sensors, nforce2, nvidia,
pmu. See /usr/portage/profiles/use*.desc for details. If
you forgot to set one of these flags, you can recompile affected packages using
the --newuse flag in emerge, see man emerge.

Configuring The Kernel

ACPI (Advanced Configuration and Power Interface) support in the kernel is
still work in progress. Using a recent kernel will make sure you'll get the
most out of it.

There are different kernel sources in Portage. I'd recommend using
gentoo-sources or tuxonice-sources. The latter contains patches
for TuxOnIce, see the chapter about sleep states
for more details. When configuring the kernel, activate at least these options:

Decide yourself whether you want to enable Software Suspend, and Sleep States
(see below). If you own an ASUS, Medion, IBM Thinkpad or Toshiba laptop, enable
the appropriate section.

The kernel has to know how to enable CPU frequency scaling on your processor.
As each type of CPU has a different interface, you've got to choose the right
driver for your processor. Be careful here - enabling Intel Pentium 4 clock
modulation on a Pentium M system will lead to strange results for example.
Consult the kernel documentation if you're unsure which one to take.

Compile your kernel, make sure the right modules get loaded at startup and boot
into your new ACPI-enabled kernel. Next run emerge sys-power/acpid to
get the acpi daemon. This one informs you about events like switching from AC
to battery or closing the lid. Make sure the modules are loaded if you didn't
compile them into the kernel and start acpid by executing /etc/init.d/acpid
start. Run rc-update add acpid default to load it on startup. You'll
soon see how to use it.

The default policy will be to enable Power Management only when needed -
running on batteries. To make the switch between AC and battery convenient,
create a runlevel battery that holds all the scripts starting and
stopping Power Management.

You can safely skip this section if you don't like the idea of having another
runlevel. However, skipping this step will make the rest a bit trickier to set
up. The next sections assume a runlevel battery exists.

# cd /etc/runlevels
# cp -a default battery

Finished. Your new runlevel battery contains everything like
default, but there is no automatic switch between both yet. Time to
change it.

Reacting On ACPI Events

Typical ACPI events are closing the lid, changing the power source or pressing
the sleep button. An important event is changing the power source, which should
cause a runlevel switch. A small script will take care of it.

First you need a script which changes the runlevel to default
respectively battery depending on the power source. The script uses the
on_ac_power command from sys-power/powermgmt-base - make sure the
package is installed on your system.

# emerge powermgmt-base

You are now able to determine the power source by executing on_ac_power
&& echo AC available || echo Running on batteries in a shell. The
script below is responsible for changing runlevels. Save it as
/etc/acpi/actions/pmg_switch_runlevel.sh.

Dont forget to run chmod +x /etc/acpi/actions/pmg_switch_runlevel.sh to
make the script executable. The last thing that needs to be done is calling the
script whenever the power source changes. That's done by catching ACPI events
with the help of acpid. First you need to know which events are
generated when the power source changes. The events are called
ac_adapter and battery on most laptops, but it might be different
on yours.

# tail -f /var/log/messages | grep "received event"

Run the command above and pull the power cable. You should see something like
this:

The interesting part is the quoted string after received event. It will
be matched by the event line in the files you are going to create below. Don't
worry if your system generates multiple events or always the same. As long as
any event is generated, runlevel changing will work.

Give it a try: Plug AC in and out and watch syslog for the "Switching to AC
mode" or "Switching to battery mode" messages. See the Troubleshooting section if the script is not able to
detect the power source correctly.

Due to the nature of the event mechanism, your laptop will boot into runlevel
default regardless of the AC/battery state. This is fine when running
from AC, but we'd like to boot into the battery runlevel otherwise. One
solution would be to add another entry to the boot loader with the parameter
softlevel=battery, but it's likely to forget choosing it. A better way
is faking an ACPI event in the end of the boot process and letting
pmg_switch_runlevel.sh script decide whether a runlevel change is
necessary. Open /etc/conf.d/local.start in your favourite editor
and add these lines:

Prepared like this you can activate Power Management policies for individual
devices.

CPU Power Management

Mobile processors can operate at different frequencies. Some allow changing
voltage as well. Most of the time your CPU doesn't need to run at full speed
and scaling it down will save much energy - often without any performance
decrease.

Some Technical Terms

CPU frequency scaling brings up some technical terms that might be unknown to
you. Here's a quick introduction.

First of all, the kernel has to be able to change the processor's frequency.
The CPUfreq processor driver knows the commands to do it on your CPU.
Thus it's important to choose the right one in your kernel. You should already
have done it above. Once the kernel knows how to change frequencies, it has to
know which frequency it should set. This is done according to the policy
which consists of a CPUfreq policy and a governor. A CPUfreq
policy are just two numbers which define a range the frequency has to stay
between - minimal and maximal frequency. The governor now decides which of the
available frequencies in between minimal and maximal frequency to choose. For
example, the powersave governor always chooses the lowest frequency
available, the performance governor the highest one. The userspace
governor makes no decision but chooses whatever the user (or a program in
userspace) wants - which means it reads the frequency from
/sys/devices/system/cpu/cpu0/cpufreq/scaling_setspeed.

This doesn't sound like dynamic frequency changes yet and in fact it isn't.
Dynamics however can be accomplished with various approaches. For example, the
ondemand governor makes its decisions depending on the current CPU load.
The same is done by various userland tools like cpudyn, cpufreqd,
powernowd and many more. ACPI events can be used to enable or disable
dynamic frequency changes depending on power source.

Setting The Frequency

Decreasing CPU speed and voltage has two advantages: On the one hand less
energy is consumed, on the other hand there is thermal improvement as your
system doesn't get as hot as running on full speed. The main disadvantage is
obviously the loss of performance. Decreasing processor speed is a trade off
between performance loss and energy saving.

Not every laptop supports frequency scaling. If unsure, have a look at the list
of supported processors in the Troubleshooting
section to verify yours is supported.

Now play around with cpufreq-set to make sure frequency switching works.
Run cpufreq-set -g ondemand for example to activate the ondemand
governor and verify the change with cpufreq-info. If it doesn't work as
expected, you might find help in the Troubleshooting
section in the end of this guide.

cpufrequtils can operate in an automatic mode (when you use the
ondemand governor), you can also switch to the userspace governor
if you want to manually set a specific speed. You can also statically set your
CPU to its highest or lowest frequency by using the performance
and powersave governors, respectively.

While cpufrequtils may be the best all-around program, there are some
other choices available in Portage. The following table gives a quick overview
of available CPU speed utilities. It's roughly separated in three categories
kernel for approaches that only need kernel support, daemon for
programs that run in the background and graphical for programs that
provide a GUI for easy configuration and changes.

Name

Category

Switch decision

Kernel governors

Further governors

Comments

'ondemand' governorKernelCPU loadN.A.N.A.
Chooses maximal frequency on CPU load and slowly steps down when the CPU is
idle. Further tuning through files in
/sys/devices/system/cpu/cpu0/cpufreq/ondemand/. Still requires
userland tools (programs, scripts) if governor switching or similar is
desired.

'conservative' governorKernelCPU loadN.A.N.A.
Unlike the ondemand governor, conversative doesn't jump to maximum
frequency when CPU load is high, but increases the frequency step by step.
Further tuning through files in
/sys/devices/system/cpu/cpu0/cpufreq/ondemand/. Still requires
userland tools (programs, scripts) if governor switching or similar is
desired.

cpudynDaemonCPU loadPerformance, powersaveDynamic
Also supports disk standby - notice however that laptop mode in most
cases will do a better job.

While adjusting the frequency to the current load looks simple at a first
glance, it's not such a trivial task. A bad algorithm can cause switching
between two frequencies all the time or wasting energy when setting frequency
to an unnecessary high level.

Which one to choose? If you have no idea about it, try cpufreqd:

# emerge cpufreqd

cpufreqd can be configured by editing /etc/cpufreqd.conf.
The default one that ships with cpufreqd may look a bit confusing. I recommend
replacing it with the one from former Gentoo developer Henrik Brix Andersen
(see below). Please notice that you need cpufreqd-2.0.0 or later. Earlier
versions have a different syntax for the config file.

Now you can start the cpufreqd daemon. Add it to the default and
battery runlevel as well.

# rc-update add cpufreqd default battery
# /etc/init.d/cpufreqd start

Sometimes it can be desirable to select another policy than the daemon chooses,
for example when battery power is low, but you know that AC will be available
soon. In that case you can turn on cpufreqd's manual mode with cpufreqd-set
manual and select one of your configured policies (as listed by
cpufreqd-get). You can leave manual mode by executing cpufreqd-set
dynamic.

Do not run more than one of the above programs at the same time. It may cause
confusion like switching between two frequencies all the time.
Verifying the result

The last thing to check is that your new policies do a good job. An easy way to
do so is monitoring CPU speed while working with your laptop:

# watch grep \"cpu MHz\" /proc/cpuinfo

If /proc/cpuinfo doesn't get updated (see Troubleshooting), monitor the CPU frequency with
sys-apps/x86info:

# watch x86info -mhz

Depending on your setup, CPU speed should increase on heavy load, decrease on
no activity or just stay at the same level. When using cpufreqd and
verbosity set to 5 or higher in cpufreqd.conf you'll get
additional information about what's happening reported to syslog.

LCD Power Management

As you can see in figure 1.1, the LCD
display consumes the biggest part of energy (might not be the case for
non-mobile CPU's). Thus it's quite important not only to shut the display off
when not needed, but also to reduce it's backlight if possible. Most laptops
offer the possibility to control the backlight dimming.

Standby settings

The first thing to check is the standby/suspend/off timings of the display. As
this depends heavily on your windowmanager, I'll let you figure it out
yourself. Just two common places: Blanking the terminal can be done with
setterm -blank <number-of-minutesM>, setterm -powersave on
and setterm -powerdown <number-of-minutesM>. For X.org, modify
/etc/X11/xorg.conf similar to this:

Probably more important is the backlight dimming. If you have access to the
dimming settings via a tool, write a small script that dims the backlight in
battery mode and place it in your battery runlevel. The following script
should work on most IBM Thinkpads and Toshiba laptops. You've got to enable the
appropriate option in your kernel (IBM Thinkpads only). For Toshiba laptops,
install sys-power/acpitool and skip configuration of thinkpad_acpi
(formerly called ibm_acpi) as described below.

Support for setting brightness is marked experimental in thinkpad_acpi. It
accesses hardware directly and may cause severe harm to your system. Please
read the thinkpad_acpi
website

To be able to set the brightness level, the thinkpad_acpi module has to be
loaded with the experimental parameter.

This should work without error messages and a file
/proc/acpi/ibm/brightness should be created after loading the
module. An init script will take care of choosing the brightness according to
the power source.

Hard disks consume less energy in sleep mode. Therefore it makes sense to
activate power saving features whenever the hard disk is not used for a certain
amount of time. I'll show you two alternative possibilities to do it. First,
laptop-mode will save most energy due to several measures which prevent or at
least delay write accesses. The drawback is that due to the delayed write
accesses a power outage or kernel crash will be more dangerous for data loss.
If you don't like this, you have to make sure that there are no processes which
write to your hard disk frequently. Afterwards you can enable power saving
features of your hard disk with hdparm as the second alternative.

Increasing idle time - laptop-mode

Recent 2.6 kernels include the so-called laptop-mode. When activated,
dirty buffers are written to disk on read calls or after 10 minutes (instead of
30 seconds). This minimizes the time the hard disk needs to be spun up.

# emerge laptop-mode-tools

laptop-mode-tools has its configuration file in
/etc/laptop-mode/laptop-mode.conf. Adjust it the way you like it,
it's well commented. Run rc-update add laptop_mode battery to start it
automatically.

Recent versions (1.11 and later) of laptop-mode-tools include a new tool
lm-profiler. It will monitor your system's disk usage and running
network services and suggests to disable unneeded ones. You can either disable
them through laptop-mode-tools builtin runlevel support (which will be reverted
by Gentoo's /sbin/rc) or use your default/battery
runlevels (recommended).

After profiling your system for ten minutes, lm-profiler will present a list of
services which might have caused disk accesses during that time.

Program: "atd"
Reason: standard recommendation (program may not be running)
Init script: /etc/init.d/atd (GUESSED)
Do you want to disable this service in battery mode? [y/N]: n

To disable atd as suggested in the example above, you would run rc-update
del atd battery. Be careful not to disable services that are needed for
your system to run properly - lm-profiler is likely to generate some
false positives. Do not disable a service if you are unsure whether it's
needed.

Limiting Write Accesses

If you don't want to use laptop-mode, you must take special care to disable
services that write to your disk frequently - syslogd is a good
candidate, for example. You probably don't want to shut it down completely, but
it's possible to modify the config file so that "unnecessary" things don't get
logged and thus don't create disk traffic. Cups writes to disk
periodically, so consider shutting it down and only enable it manually when
needed.

# rc-update del cupsd battery

You can also use lm-profiler from laptop-mode-tools (see above) to find
services to disable. Once you eliminated all of them, go on with configuring
hdparm.

hdparm

The second possibility is using hdparm. Skip this if
you are using laptop-mode. Otherwise, edit /etc/conf.d/hdparm and
add the following values to your drive entries. This example assumes your hard
drive is called hda:

hda_args="-q -S12"

This will activate power management for your hard drive. If you ever want to
deactivate power management, you can edit /etc/conf.d/hdparm and
change the values to -q -S0, or just run hdparm -q -S0 /dev/hda.

See man hdparm for the options. Though you can always start hdparm
manually when you are on battery power by running /etc/init.d/hdparm
start, it's much easier to automate its startup and shutdown. To do so, add
hdparm to the battery runlevel so that it will automatically enable power
management.

# rc-update add hdparm battery

Be careful with sleep/spin down settings of your hard drive. Setting it to
small values might wear out your drive and lose warranty.
Other tricks

Another possibility is to deactivate swap in battery mode. Before writing a
swapon/swapoff switcher, make sure there is enough RAM and swap isn't used
heavily, otherwise you'll be in big problems.

If you don't want to use laptop-mode, it's still possible to minimize disk
access by mounting certain directories as tmpfs - write accesses are not
stored on a disk, but in main memory and get lost with unmounting. Often it's
useful to mount /tmp like this - you don't have to pay special
attention as it gets cleared on every reboot regardless whether it was mounted
on disk or in RAM. Just make sure you have enough RAM and no program (like a
download client or compress utility) needs extraordinary much space in
/tmp. To activate this, enable tmpfs support in your kernel and
add a line to /etc/fstab like this:

none /tmp tmpfs size=32m 0 0

Pay attention to the size parameter and modify it for your system. If you're
unsure, don't try this at all, it can become a performance bottleneck easily. In
case you want to mount /var/log like this, make sure to merge the
log files to disk before unmounting. They are essential. Don't attempt to mount
/var/tmp like this. Portage uses it for compiling...
Power Management For Other DevicesGraphics Cards

In case you own an ATI graphics card supporting PowerPlay (dynamic clock
scaling for the graphics processing unit GPU), you can activate this
feature in X.org. Open /etc/X11/xorg.conf and add (or enable) the
DynamicClocks option in the Device section. Please notice that this
feature will lead to crashes on some systems.

Section "Device"
[...]
Option "DynamicClocks" "on"
EndSection

Wireless Power Management

Wireless LAN cards consume quite a bit of energy. Put them in Power Management
mode just like your hard drives.

This script assumes your wireless interface is called wlan0; replace
this with the actual name of your interface.

Add the following option to /etc/conf.d/net to automatically enable
power management for your wireless card:

iwconfig_wlan0="power on"

See man iwconfig for details and more options like the period between
wakeups or timeout settings. If your driver and access point support changing
the beacon time, this is a good starting point to save even more energy.

USB Power Management

There are two problems with USB devices regarding energy consumption: First,
devices like USB mice, digital cameras or USB sticks consume energy while
plugged in. You cannot avoid this (nevertheless remove them in case they're not
needed). Second, when there are USB devices plugged in, the USB host controller
periodically accesses the bus which in turn prevents the CPU from going into
sleep mode. The kernel offers an experimental option to enable suspension of
USB devices through driver calls or one of the power/state files
in /sys.

They can be called whenever the system is not in use, but a shutdown is not
wanted due to the long boot time.

Sleep (S3)

The ACPI support for these sleep states is marked experimental for good reason.
APM sleep states seem to be more stable, however you can't use APM and ACPI
together.

Power Management Options --->
[*] Power Management support
[*] Suspend to RAM and standby

Once your kernel is properly configured, you can use the
hibernate-script to activate suspend or sleep mode. Let's install that
first.

# emerge hibernate-script

Some configuration has to be done in /etc/hibernate. The default
package introduces a few configuration files for each sleep state. Options that
are common to all suspend methods are placed in common.conf; make
sure this file is properly set up for your system.

To configure sleep, edit sysfs-ram.conf in
/etc/hibernate. UseSysfsPowerState mem is already setup
correctly, but if you need to make further changes to this particular sleep
state (or any other sleep state) you should add them to
/etc/hibernate/hibernate.conf. The comments and option names will
guide you. If you use nfs or samba shares over the network, make sure to
shutdown the appropriate init scripts to avoid timeouts.

For more information on setting up sleep states, read man
hibernate.conf.

Ready? Now is the last chance to backup any data you want to keep after
executing the next command. Notice that you probably have to hit a special key
like Fn to resume from sleep.

# hibernate-ram

If you're still reading, it seems to work. You can also setup standby (S1) in a
similar way by editing sysfs-ram.conf and changing
"UseSysfsPowerState mem" to "UseSysfsPowerState standby". S3 and S4 are the more
interesting sleep states due to greater energy savings however.

Hibernate (S4)

This section introduces hibernation, where a snapshot of the running system is
written to disk before powering off. On resume, the snapshot is loaded and you
can go on working at exactly the point you called hibernate before.

Don't exchange non hot-pluggable hardware when suspended. Don't attempt to load
a snapshot with a different kernel image than the one it was created with.
Shutdown any NFS or samba server/client before hibernating.

There are two different implementations for S4. The original one is swsusp,
then there is the newer tuxonice (formerly suspend2) with a nicer interface
(including fbsplash support). A feature comparison is
available at the tuxonice homepage.
There used to be Suspend-to-Disk (pmdisk), a fork of swsusp, but it has been
merged back.

TuxOnIce is not included in the mainline kernel yet, therefore you either have
to patch your kernel sources with the patches provided by tuxonice.net or use
sys-kernel/tuxonice-sources.

The configuration for swsusp is rather easy. If you didn't store the location
of your swap partition in the kernel config, you can also pass it as a
parameter with the resume=/dev/SWAP directive. If booting is not
possible due to a broken image, use the noresume kernel parameter. The
hibernate-cleanup init script invalidates swsusp images during the boot
process.

# rc-update add hibernate-cleanup boot

To activate hibernate with swsusp, use the hibernate script and set
UseSysfsPowerState disk in /etc/hibernate/sysfs-disk.

Backup your data before doing this. Run sync before executing one of the
commands to have cached data written to disk. First try it outside of X, then
with X running, but not logged in.

If you experience kernel panics due to uhci or similar, try to compile USB
support as module and unload the modules before sending your laptop to sleep
mode. There are configuration options for this in common.conf

The following section discusses the setup of TuxOnIce including fbsplash support
for a nice graphical progress bar during suspend and resume.

The first part of the configuration is similar to the configuration of swsusp.
In case you didn't store the location of your swap partition in the kernel
config, you have to pass it as a kernel parameter with the
resume=swap:/dev/SWAP directive. If booting is not possible due to a
broken image, append the noresume parameter. Additionally, the
hibernate-cleanup init script invalidates TuxOnIce images during the boot
process.

# rc-update add hibernate-cleanup boot

Now edit /etc/hibernate/tuxonice.conf, enable the TuxOnIce
options you need. Do not enable the fbsplash options in
common.conf just yet.

Please configure fbsplash now if you didn't do already. To enable
fbsplash support during hibernation, the sys-apps/tuxonice-userui package
is needed. Additionally, you've got to enable the fbsplash USE flag.

The ebuild tells you to make a symlink to the theme you want to use. For
example, to use the livecd-2005.1 theme, run the following command:

# ln -sfn /etc/splash/livecd-2005.1 /etc/splash/tuxonice

If you don't want a black screen in the first part of the resume process, you
have to add the tuxoniceui_fbsplash tool to your initrd image. Assuming
you created the initrd image with splash_geninitramfs and saved it as
/boot/fbsplash-emergence-1024x768, here's how to do that.

Afterwards adjust grub.conf (or lilo.conf) so that
your TuxOnIce kernel uses
/boot/fbsplash-tuxonice-emergence-1024x768 as initrd image. You can
now test a dry run to see if everything is setup correctly.

# tuxoniceui_fbsplash -t

Afterwards open /etc/hibernate/common.conf and activate the
fbsplash options. Execute hibernate and enjoy.

Troubleshooting

Q: I'm trying to change the CPU frequency, but
/sys/devices/system/cpu/cpu0/cpufreq/scaling_governor does not
exist.

A: Look for ACPI related error messages with dmesg | grep ACPI.
Try to update the BIOS, especially if a broken DSDT is reported. You can also
try to fix it yourself (which is beyond the scope of this guide).

Q: My laptop supports frequency scaling, but according to
/proc/cpuinfo the speed never changes.

A: Probably you have activated symmetric multiprocessing support
(CONFIG_SMP) in your kernel. Deactivate it and it should work. Some older
kernels had a bug causing this. In that case, run emerge x86info, update
your kernel as asked and check the current frequency with x86info -mhz.

Q: I can change the CPU frequency, but the range is not as wide as in
another OS.

A: You can combine frequency scaling with ACPI throttling to get a lower
minimum frequency. Notice that throttling doesn't save much energy and is mainly
used for thermal management (keeping your laptop cool and quiet). You can read
the current throttling state with cat /proc/acpi/processor/CPU/throttling
and change it with echo -n "0:x" > /proc/acpi/processor/CPU/limit, where
x is one of the Tx states listed in
/proc/acpi/processor/CPU/throttling.

Q: When configuring the kernel, powersave, performance and userspace
governors show up, but that ondemand thing is missing. Where do I get it?

A: The ondemand governor is only included in recent kernel sources. Try
updating them.

Q: Battery life time seems to be worse than before.

A: Check your BIOS settings. Maybe you forgot to re-enable some of the
settings.

Q: My battery is charged, but KDE reports there would be 0% left and
immediately shuts down.

A: Check that battery support is compiled into your kernel. If you use
it as a module, make sure the module is loaded.

A: This message is generated by the /etc/acpi/default.sh
script that is shipped with acpid. You can safely ignore it. If you like to get
rid of it, you can comment the appropriate line in
/etc/acpi/default.sh as shown below:

Q: I want to use TuxOnIce, but it tells me my swap partition is too
small. Resizing is not an option.

A: If there is enough free space on your system, you can use the
filewriter instead of the swapwriter. The hibernate-script supports it as
well. More information can be found in
/usr/src/linux/Documentation/power/tuxonice.txt.

Q: I just bought a brand new battery, but it only lasts for some
minutes! What am I doing wrong?

A: First follow your manufacturer's advice on how to charge the battery
correctly.

Q: The above didn't help. What should I do then?

A: Some batteries sold as "new" are in fact old ones. Try the following: